1 . Sitting back in my seat, I can’t quite believe that I’m about to travel along the railway that many foreign experts ______was “impossible”. The train has been racing along steadily since it left Xining. All this time, the song “Sky Railway” has been playing inside my head. The words “railways like massive dragons are ______among the mountains” seem particularly vivid as I travel across the “roof of the world”.

I was one of the people who came from all parts of China to work on this railway.Taking years to complete, the Qinghai-Tibet Railway is a record of all of our efforts to overcome the most difficult engineering challenges. How to protect the ______ ecosystem was among the top ______.

The first landmark to catch my eye is the splendid Qingshuihe Bridge, the world’s longest bridge built over permafrost(永冻土层). Look! A group of Tibetan antelopes is moving under the bridge, with some stopping to eat grass ______their leisure. Thirty-three passages have been built under the railway to allow the animals to move safely and freely in their natural _____. Wild animals have now been using these passages for years. They seem totally _____ that we are _______past at over 100 kilometres an hour.We even moved 140,000 square metres of wetland to a new area in order to protect its ______ecosystem.

The journey has been flying by, and ______ I know it, we have reached Tanggula Station. _____at over 5,000 metres above sea level, this is the highest railway station in the world. In locations such as this, the thin air, changeable weather and high levels of UV radiation presented perhaps the greatest challenge for railway workers. To make sure we stayed healthy, several oxygen-making stations were ______.

As we pass Cuona Lake, I feel a sense of _____and achievement. Using thousands and thousands of sandbags, we built a twenty-kilometre wall along the lake to protect it from construction waste. Cuona Lake is so close to the railway that I want to reach out and touch its pale blue mirror-like surface.

The Qinghai-Tibet Plateau has been attracting people’s ______ for centuries. Now,______our efforts, passengers from all over the country have been enjoying these magical landscapes. I am proud that we built our “impossible” railway, and did so with the care that the environment deserves. It truly is an extraordinary “Sky Railway”.